1. Field of the Invention
The present invention relates to an electrostatic precipitator to be used in a power plant, a cement plant, an industrial waste incinerator, a road or a tunnel for removing floating particles or radioactive dust, or for cleaning indoor air.
2. Description of the Related Art
An electrostatic precipitator ionizes (charges) fine particle such as dust floating in a gas by applying a high voltage to the gas (or by a corona discharge). The charged particles may then be collected on dust-collecting electrodes of the electrostatic precipitators, by making use of an electric field, to remove the particles (hereinafter referred to as "dust") from the gas. An electrostatic precipitator can collect the particles of most kinds of solids and liquid highly efficiently. In addition, the maintenance and running of the electrostatic precipitator is relatively inexpensive because it has a simple construction and few moving parts. However, the electrostatic precipitator has drawbacks in that its entire structure is large-sized due to the large space where dust is collected, and its construction cost may be raised by expensive parts such as a DC high voltage supply or a high voltage insulator. In addition, its dust collecting performance is determined by the electric resistivity of the dust. (Reference should be made to pp. 1119 to 1121 of Handbook of Electric Engineering, edited by Association of Electricity and issued by OHM Co., Ltd. on Jul. 10, 1983).
The present inventor has already introduced small-sized electrostatic precipitators having a high dust collecting efficiency in the inventions described in Japanese patent Application No. Hei 6-51312 and Japanese patent Application No. Hei 6-132548. The features of those apparatus will be briefly described below.
The electrostatic precipitator shown in FIG. 7, includes rectangular plate shaped metal discharge electrodes 101 formed with a series of saw-toothed portions having tips 101a on the edges thereof; and dust-collecting electrodes 102 formed with a number of pores 102a in their faces. The dust-collecting electrodes 102 are arranged so that their faces are parallel, and the dust-collecting electrodes 102 are connected through spacers 103 (103a, 103b and 103c) to form dust-collecting electrode groups 104. The discharge electrodes 101 are also arranged so that their faces are parallel, and they are connected through spacers 105 (105a and 105b) to form discharge electrode groups 106. These dust-collecting electrode groups 104 and discharge electrode groups 106 are fixed to a frame (not shown) by means of screws 107 extending from the spacers 103 and 105. A gas carrying dust particles is introduced in the direction of the arrow into the apparatus.
This apparatus features pores 102a in the dust-collecting electrodes 102 that cause a current A from the discharge electrodes 101 to be centralized at portions other than the pores 102a on the dust-collecting electrodes 102, as indicated by the arrows in FIG. 8. This increases the current density at the solid portions of the dust-collecting electrodes 102. As a result, a high dust-collecting efficiency is achieved. In addition, an air flow is established through the pores 102a of the dust-collecting electrodes 102, as shown by the arrows in FIG. 9. Dust particles collected on the electrode are rubbed off by the air flow, which prevents deterioration of the dust collecting ability of the apparatus due to dust built-up.
On the other hand, the electrostatic precipitator shown in FIG. 10 is modified such that the dust-collecting electrodes 102 of FIG. 7 are replaced by steel pipes 108. These pipes 108 are supported by steel beams 109, which may be positioned at the upper, lower or intermediate portions of the pipes 108, if necessary. In this apparatus, the pipes 108, acting as the dust-collecting electrodes, have curved faces which causes collected dust particles to drop by their own weight before dust becomes highly deposited. As a result, the dust-collecting electrodes have their surfaces covered with the dust for only short time periods, and the dust collecting efficiency of the apparatus is enhanced.
Because the electrostatic precipitator shown in FIG. 7 is assembled using numerous spacers, the high number of parts seriously increases the number of steps required for assembly. In addition, because the dust-collecting electrodes have to be manufactured into the desired shape before being attached, their manufacturing steps are troublesome. In the apparatus shown in FIG. 10, on the other hand, the steel beams 109 have to be prepared because they are used to support the pipes 108.